1. Field of the Invention
The present invention relates to a display device having a diffraction grating to separate an incident light into color light components to establish color separation and a transmission type light valve such as liquid crystal panel to receive the diffracted light for realizing a color display. The present invention also relates to a display device having a light source adapted to provide parallel light beams to a diffraction grating. The present invention also relates to a display device having a diffraction grating to separate an incident light into color light components and a polarization separation means enabling the separated light to be used.
2. Description of the Related Art
A color display device comprises a light valve such as a liquid crystal panel which has a color filter having red, green and blue portions. The display device also has display electrodes corresponding to the red, green and blue portions of the color filter, so that a light passing through a certain color portion passes through the corresponding display electrode or is blocked by the corresponding display electrode by controlling a voltage on or off. The color filter allows a light component having a particular color bandwidth of wavelength to pass therethrough and does not allow the remaining light components therethrough, the remaining light components being reflected or absorbed. Therefore, a viewer can see the transmitted light component having a particular color bandwidth or wavelength. A problem in this type of color display device resides in that a portion of the light which passes through the color filter is used but the remaining portion of the light is not used.
A color display device using a diffraction grating, in place of a color filter, is disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 62-293222 and No. 62-293223.
The diffraction grating separates an incident light such as natural light into a diffracted light of a zeroth order which is not substantially diffracted, a diffracted light of first order having different color light components having respective color bandwidths or wavelengths, a diffracted light of second order and so on. If the diffracted light of zeroth order and diffracted light of first order can be effectively used, it is expected that efficiency of available light can be increased, compared with the case using the color filter. However, it is difficult to match the diffracted light of zeroth order and the diffracted light of first order with the pitch of the display electrodes, since the diffracted light of zeroth order and the diffracted light of first order emerge from the diffraction grating at different angles. If a portion of the diffracted light of zeroth order and the diffracted light of first order is not used for display and emerges from the display device in an uncontrolled manner, an image with high quality cannot be realized.
In the above described Japanese Unexamined Patent Publication (Kokai) No. 62-293222, the display electrodes of the liquid crystal panel are formed so that light components having red, green and blue bandwidth or wavelength of the diffracted light of first order pass through the display electrodes and the diffracted light of zeroth order is directed to a shading portion of the liquid crystal panel. In this case, the shading portion is arranged at a position between the red, green and blue display electrodes of one picture element or at a position just adjacent to the red, green and blue display electrodes of one picture element.
Therefore, the diffracted light of zeroth order and the diffracted light of first order are made incident to a region within one picture element. However, it is difficult to arrange that the diffracted light of zeroth order and the diffracted light of first order impinge against the surface of the liquid crystal panel at a constant pitch, since the angle between the diffracted light of zeroth order and the diffracted light of first order is different from angles between the light components of the diffracted light of first order. Therefore, it is difficult to form the respective color display electrodes of one picture element so that the display electrodes have an identical shape and are arranged at a constant pitch. Therefore, it is difficult to form many, small picture elements within a certain display area. In addition, if the diffracted light of first order on the xc2x1 sides is to be used, the difference of the incident angle to the liquid crystal panel becomes larger.
In the above described Japanese Unexamined Patent Publication (Kokai) No. 62-293223, light components having red and blue bandwidths or wavelength of the diffracted light of first order passing through the diffraction grating are used but the light component having the green bandwidth of wavelength of the diffracted light of first order is not used. The diffracted light of zeroth order is used to realize a green color. However, the incident light must include a large amount of the light component having the green bandwidth or wavelength since the diffracted light of zeroth order is substantially identical to the incident light made incident to the diffraction grating, so the amounts of the light components having red and blue bandwidths or wavelength of the diffracted light of first order is reduced.
Also, in this case too, it is difficult for the diffracted light of the zeroth order and the diffracted light of the first order to impinge against the surface of the liquid crystal panel at a constant pitch, since the angle between the diffracted light of zeroth order and the diffracted light of first order is different from angles between the light components of the diffracted light of first order. Therefore, it is difficult to obtain a display device with high definition. In this case, particularly, the light component having the green bandwidth or wavelength of the diffracted light is shaded, but this light component is located at the center of the region in which the diffracted light of first order is distributed. Therefore, the shading portion must be provided in a narrow region between the red and blue display electrodes.
In the display device having the diffraction grating to separate an incident light into color light components, it is desirable that light beams are as parallel as possible to each other and parallel beams are made incident to the diffraction grating.
In the liquid crystal display device, a polarizer and an analyzer are usually used with a liquid crystal panel. However, the polarizer absorbs approximately one half of the light provided by the light source, and generates heat by absorbing the light. Particularly, in the projection type display device, it is necessary to use a strong light source, so the amount of heat generated by the polarizer increases and it is necessary to cool the polarizer.
The polarizer absorbs approximately one half of the light from the source, and the absorbed light is not used, so the efficiency of the available light is reduced. Therefore, means for improving the efficiency of the available light is required. For example, Japanese Unexamined Patent Publication (Kokai) No. 6-324329 discloses a liquid crystal display device having a polarization beam splitter and an array of micro-lenses. According to this arrangement, it is possible to use both the P-polarized light and the S-polarized separated by the polarization beam splitter. However, it is further desired to more and more effectively use the separated P- and S-polarized lights.
The object of the present invention is to provide a display device having a diffraction grating which can realize a high definition display, by effectively treating a diffracted light of zeroth order and a diffracted light of first order passing through the diffraction grating.
Another object of the present invention is to provide a projection type display device having a diffraction grating and a light source which can supply light beams as parallel as possible to the diffraction grating.
A further object of the present invention is to provide a display device in which the disposition of display dots is improved to provide a high definition display.
According to one aspect of the present invention, there is provided a display device having a diffraction grating arranged such that a diffracted light of the zeroth order and a diffracted light of the first order having different color light components emerge from the diffraction grating, a condenser means, and a light valve arranged to receive the light passing through the diffraction grating and the condenser means to modulate the light to form an image. The light valve has a plurality of minute unit regions, each unit region including a plurality of color display dots, the display dots in each unit region being arranged in a vertical relationship and in the order of wavelength of the light. An incident angle of the diffracted light of zeroth order made incident to the light valve is greater than incident angles of the color light components of diffracted light of first order made incident to the light valve. The diffracted light of first order diffracted at a certain area of the diffraction grating passes through the display dots in one unit region. The diffracted light of the zeroth order passing through said certain area of the diffraction grating passes through a different unit region from said one unit region.
In this arrangement, the display dots in one unit region constitute one picture element. The diffracted light of the zeroth order passes through the different unit region from the unit region through which the diffracted light of first order passes. Therefore, the diffracted light of the zeroth order passes through the light valve at a greater angle relative to the normal to the display surface, and the diffracted light of first order passes through the light valve at a smaller angle relative to the normal to the display surface. Therefore, it is possible to arrange the display device such that the angles between the different color light components of the diffracted light of first order are identical to each other and the display dots of the light valve are thus arranged at a constant pitch and have an identical size. Since the diffracted light of the zeroth order passes through the light valve at a greater angle relative to the normal to the display surface, a viewer does see the diffracted light of zeroth order within a usual field of vision and the display produced by the diffracted light of first order is not affected by the diffracted light of zeroth order. Therefore, it is possible to obtain a display device with high quality and high definition.
In particular, the display dots in each unit region are arranged in the vertical relationship and in the order of wavelength of the light. By the arrangement in this manner, the diffracted light of zeroth order passes obliquely upward or obliquely downward through the light valve. In the display device, a viewing angle in one direction in which a good image can be seen is relatively wide but a viewing angle in the other direction perpendicular to the former one direction in which a good image can be seen is relatively narrow. It is usual that the direction in which the viewing angle is wide is arranged horizontally, and the direction in which the viewing angle is narrow is arranged vertically. Therefore, the diffracted light of zeroth order passes obliquely upward or obliquely through the liquid crystal panel, so the light travels outside the fundamentally narrow viewing angle.
Preferably, the diffracted light of first order include red, green, and blue light components, and the diffracted light of the zeroth order passing through said certain area of the diffraction grating passes through the next and next unit region from said one unit region. The angular relationship between the diffracted light of the zeroth order and the diffracted light of first order in this arrangement is advantageous in obtaining a high definition display.
Preferably, the diffracted light of first order includes red, green, and blue light components, and the green light component of the diffracted lights of first order is made incident to the light valve substantially perpendicular to the latter. By this arrangement, all the color light components can be made incident to the light valve at angles as close as possible to the normal to the display surface.
Preferably, the condenser means includes a condenser lens having condenser elements corresponding to the unit regions of the light valve, for example, an array of micro-lenses and is arranged in front of the diffraction grating or between the diffraction grating and light valve. Alternatively, the condenser means has condenser elements corresponding to the unit regions of the light valve and incorporated in the diffraction grating. The condenser lens causes the light travelling from the diffraction grating to the light valve to be condensed on each display dot, to increase the efficiency of available light.
Preferably, the light valve includes at least one liquid crystal panel, and it is possible to provide a high definition display device which is thin.
As one of the arrangements for arranging the display dots in the order of wavelength of the light and in the vertical relationship, it is advisable to arrange such that the upper display dot provides a longer wavelength and the lower display dot provides a shorter wavelength. By this arrangement, the diffracted light of the zeroth order passes obliquely through the light valve. Alternatively, it is advisable to arrange such that the upper display dot provides a shorter wavelength and the lower display dot provides a longer wavelength. By this arrangement, the diffracted light of zeroth order passes obliquely upward through the light valve.
Preferably, said display device includes an upper part and a lower part, and said display dots are arranged so that in the lower part, the diffracted light of the zeroth order emerges downward from the light valve, and in the upper part, the diffracted light of the zeroth order upwardly emerges the light valve.
Preferably, in this case, said display device is formed in a multi-panel structure comprising a plurality of liquid crystal panels.
A display device according to another feature of the present invention includes a diffraction grating arranged such that a diffracted light of the zeroth order and a diffracted light of the first order having different color light components emerge from the diffraction grating, a condenser means, and a light valve arranged to receive the light passing through the diffraction grating and the condenser means to modulate the light to form an image. The light valve has a plurality of minute unit regions, each unit region including a plurality of color display dots and an additional display dot. The display dots in each unit region are arranged in the order of wavelength of the light. An incident angle of the diffracted light of zeroth order made incident to the light valve is greater than incident angles of the color light components of the diffracted light of first order made incident to the light valve. The diffracted light of first order diffracted at a certain area of the diffraction grating passes through said the display dots in one unit region, and the diffracted light of the zeroth order passing through said certain area of the diffraction grating passes through the additional display dot in the different unit region from said one unit region.
In this arrangement too, the diffracted light of the zeroth order passes through the different unit region from the unit region through which the diffracted light of the first order passes, and the diffracted light of the zeroth order passes through the light valve at a greater angle relative to the normal to the display surface. Therefore, it is possible to obtain a high definition display device. Also, in this case, the diffracted light of the zeroth order can be used.
A display device according to a further feature of the present invention includes a diffraction grating arranged such that a diffracted light of the zeroth order and a diffracted light of the first order having different color light components emerge from the diffraction grating, a condenser means, and a light valve arranged to receive the light passing through the diffraction grating and the condenser means to modulate the light to form an image. The light valve having a plurality of minute unit regions, each unit region including a plurality of color display dots and a shading portion. The display dots in each unit region are arranged in the order of wavelength of the light. An incident angle of the diffracted light of the zeroth order made incident to the light valve is greater than incident angles of the diffracted light of the first order made incident to the light valve. The diffracted light of the first order diffracted at a certain area of the diffraction grating passes through the display dots in one unit region, and the diffracted light of the zeroth order passing through said certain area of the diffraction grating passes through the shading portion in the different unit region from said one unit region.
In this arrangement too, the diffracted light of the zeroth order passes through the different unit region from the unit region through which the diffracted light of the first order passes, and the diffracted light of the zeroth order passes through the light valve at a greater angle relative to the normal to the display surface. Therefore, it is possible to obtain a high definition display device. Also, in this case, the diffracted light of the zeroth order is positively shaded by the shading portion, and a light leaking problem does not occur.
Preferably, the diffracted light of first order includes red, green, and blue light components, and the diffracted light of the zeroth order passing through said certain area of the diffraction grating passes through the shading portion in the unit region located next to said one unit region.
A projection type display device according to a further feature of the present invention includes a light source, an optical device having an aperture for converting beams of light emerging from said light source into parallel beams, a diffraction grating member arranged to receive the light passing through said optical device, a light valve arranged to receive the light passing through the diffraction grating member to modulate the light to form an image, and a projection lens for projecting the image formed by the light valve.
By providing the optical device having the aperture for converting beams of light emerging from said light source into parallel beams, light having a high degree of parallelism can be made incident to the diffraction grating and color separation by the diffraction grating can be reliable carried out. Therefore, it is possible to obtain a projection type display device having a splendid color purity.
A display device according to a further feature of the present invention includes a source of light, a polarization separating means, a condenser lens, a light valve arranged to receive the light passing through the condenser lens to modulate the light to form an image, and an analyzer. The polarization separating means comprises a polarization separating film for separating the light into P-polarized light and S-polarized light based on transmission and reflection, and a reflection mirror for reflecting the polarized light passing through or reflected by the polarization separating film, the polarized light passing through or reflected by the polarization separating film toward the reflection mirror and the polarized light reflected by the reflection mirror form a polarization separating angle therebetween and travel toward the condenser lens.
A display device according to a further feature of the present invention includes a source of light, a polarization separating means, a condenser lens, a light valve arranged to receive the light passing through the condenser lens to modulate the light to form an image, and an analyzer. The polarization separating means comprises a material formed in a prism-shaped cross-sectional shape and having birefringence.
A display device according to a further feature of the present invention includes a first diffraction grating, a second diffraction grating, and a polarization converting means arranged between the first and second diffraction gratings, whereby a polarization separation and a color separation can be carried out.
A display device according to a further feature of the present invention includes a plurality of picture elements, each picture element having three display dots arranged adjacent to each other. A disposition of triangles formed of segments connecting the centers of the three display dots or the centers of apertures of the three display dots is a tetragonal disposition in which triangles are arranged at constant pitches in the mutually perpendicular first and second directions.
A display device according to a further feature of the present invention includes a diffraction grating member and a light valve arranged to receive the light passing through the diffraction grating member to modulate the light to form an image. The light valve has a plurality of display dots defined by apertures of a shading layer, the display dots being identically shaped to each other, the shape of one display dot is symmetrical with respect to first and second mutually perpendicular lines passing through the center of said one display dot.
A display device according to a further feature of the present invention includes a diffraction grating member, and a light valve arranged to receive the light passing through the diffraction grating member to modulate the light to form an image. The light valve has a plurality of picture elements, each picture element having three display dots arranged adjacent to each other. Each display dots is defined by an aperture of a shading layer, one of three display dots having an aperture area smaller than that of the remaining display dots.